The present invention relates to a method of electroplating copper capable of effectively preventing the adhesion of particles onto a plating object, particularly onto a semiconductor wafer during copper electroplating, a phosphorous-containing copper anode for use in such copper electroplating, and a semiconductor wafer comprising a copper layer with low particle adhesion formed by the foregoing copper electroplating.
Copper electroplating is generally used for copper wiring fabrication in a PWB (print wiring board) or the like, but recently, it comes to be used for copper wiring fabrication of a semiconductor. Copper electroplating has a long history, and has reached its current state after numerous technical backlogs. However, with the use of copper electroplating for copper wiring fabrication of a semiconductor, new drawbacks which were not found with PWBs have arisen.
When performing copper electroplating, phosphorous-containing copper is generally used as the anode. This is because if an insoluble anode prepared from platinum, titanium, iridium oxide or the like is used, the additive agent in the plating solution is affected by anode oxidation and decomposes, whereby defective plating occurs. Meanwhile, when electrolytic copper or oxygen-free copper as a soluble anode is used during the dissolution, particles such as sludge containing metallic copper and copper oxide arose from the dismutation reaction of monovalent copper are generated, and the plating object may become contaminated.
Meanwhile, if a phosphorous-containing copper anode is used, a black film formed from copper phosphide, copper chloride or the like is formed on the anode surface by way of electrolysis, and this is used to prevent the generation of metallic copper or copper oxide arose from the dismutation reaction of monovalent copper, and enables the formation of a copper layer with low adhesion of particles.
Nevertheless, even if a phosphorous-containing copper is used as the anode as described above, because of the fall off of the black film or the generation of metallic copper or copper oxide at the thin portion of the black film, the generation of particles is not completely prevented.
In light of the above, the anode is usually wrapped with a filter fabric known as an anode bag in order to prevent particles from reaching the plating solution. However, when this kind of method is applied to plating, particularly to plating on a semiconductor wafer, fine particles that were not found in the wiring fabrication on the PWB and the like will reach the semiconductor wafer, and there is a problem in that such fine particles adhere to the semiconductor and cause defective plating.
The present inventors have proposed several methods of solution to solve the foregoing problems (refer to Patent Documents 1 to 4). These methods yield the effect of dramatically reducing the generation of particles compared to the conventional plating on a semiconductor wafer using a phosphorous-containing copper anode. However, a problem of the generation of fine particles to some degree has still remained even by the forgoing solution.    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2000-265262    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2001-98366    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2001-123266    [Patent Document 4] Japanese Patent Laid-Open Publication No. 1991-180468